He did assert that he could transmit a LOT of electrical energy wirelessly, and he convinced some well-heeled investors to finance him for some time while he developed that idea. But it never panned out -- not even close -- and I'm not aware of any trained physicist or electrical engineer who believes that Tesla's approach is possible today. High power wireless transmission of electrical energy requires close magnetic coupling or very high frequency (microwave) and directional antennas. Dangerous to anybody who gets in the way of the beam, and difficult to convert back to a more useable form - - say, to power an electric motor.
In his later days he was a weirdo and a con man. I don't know of any documentation that supports the notion that Tesla was "done in" by the establishment because he and his ideas posed a credible threat to their electrical monopoly and profits.
Here's the electrochemical whiz kid demonstrating a few different means of wirelessly transmitting power. At 11:33 he explicitly refutes the notion that Tesla could have gotten free electrical energy from the air.
No + and - designation on the input power terminals of a device that is AC powered, such as that bulb. In an Alternating Current (AC) circuit the current flow reverses every cycle. So half the time the current is flowing into one terminal and out the other, and half the time out one and into the other. No + and -; both terminals get a ~.
BTW, I have the exact same model multimeter as Whiz Kid -- a Fluke 87 V. (Imagine discovering that Nikolai Lugansky plays the same model Bechstein 212 that you practice on at home.)
Coolo. So it's thus on any household device with standard 2-prong plug? But why do some have one prong slitely bigger than the other, and lots have a third -- that I feel sure I've heard called the ground connection?
Tried this in wikid -- sez "The plug is a male connector, often with protruding pins that match the openings and female contacts in a socket." Greek to me!
On a 2-prong plug, one blade is wider than the other so that the plug can be inserted only one way. This polarization is for safety; it ensures that the outlet's "hot" wire -- the wire that has on it 120 volts with respect to ground -- gets connected to the appliance correctly, i.e. to the appliance's on/off switch so that when switched off no downstream part of the circuit carries 120 volts. In the case of a lamp, this polarization ensures that the outer screw base, which is easy to touch when replacing a bulb, is never hot, even if the lamp is plugged in and turned on when you change the bulb. Some devices are inherently safer than others; a common AC adapter for say a computer or a phone charger will sometimes have a non-polarized plug because there is little danger of user exposure to high voltage.
A 3-prong plug has a ground pin. This provides extra safety, and is used for a device that has a metal enclosure. If an internal fault causes the hot wire to contact the metal, then current will flow through the 3rd prong back to "ground" at the circuit panel (and trip the circuit breaker) rather than through the user. For some devices the ground terminal also provides some other advantages.